Linear drive

ABSTRACT

An apparatus for producing linear motion from rotary motion is disclosed comprising a drive rod ( 10 ) of circular cross section which is arranged to be rotated at a constant speed in the same direction. A carriage ( 11 ) which is arranged to be mounted on the rod for axial movement along the length thereof is provided with at least one roller member ( 12   a,    12   b ) arranged to engage the rod at an angle to the axis of rotation of the rod. The rotary motion of the red then causes the roller member to rotate, thereby generating an axial rector component in a direction along the rod, thus causing the carriage to move in a linear direction along the rod.

TECHNICAL FIELD

The present invention relates to apparatus for producing linear motion,and more particularly to producing linear motion from rotary motion.

BACKGROUND ART

Linear motion can be produced using a large number of differentmechanisms, and a wide range of such mechanisms will be apparent tothose skilled in the art. Furthermore, a wide range of mechanisms whichmore specifically convert a rotary motion into a linear motion will alsobe known, and have found application in many different technical fields.

SUMMARY OF THE INVENTION

It is an object of the present invention that linear motion needs to becreated with very simply controlled apparatus without requiringcomplicated gearing or switching systems. The linear motion is to beproduced from rotary motion in a single direction.

In order to meet the above object, the present invention provides for anelongate drive rod of circular cross-section which is arranged to berotated at a constant speed in the same direction. A carriage which isarranged to be mounted on the rod for axial movement along the length ofthe rod is provided with at least one roller member disposed with itsaxis of rotation at an angle to the perpendicular to the axis ofrotation of the rod, and arranged to be pressed into contact with thesurface of the rod by an actuator. The rotary motion of the rod causesthe roller member to rotate about its axis, the direction of rotationcausing a component vector to arise in an axial direction along the rod,thereby moving the carriage and roller along the elongate rod.

According to the present invention, there is provided an apparatus forproducing linear motion comprising:

an elongate rod of circular cross-section arranged to be continuouslyrotated in a first direction about an elongate axis; and

a carriage arranged to be mounted on the rod so as to permit axialmovement of the carriage along the length of the rod;

wherein the carriage comprises:

at least one first roller member arranged to contact the rod such thatan axis of rotation of said roller member is at a first angle to theaxis of rotation of the rod; and

at least one first actuator means for pressing the first roller memberagainst the rod to cause rotation of the roller member;

wherein the rotation of the roller member generates at least one axialvector in a first axial direction along said rod whereby to cause axialmovement of the carriage along the rod in said first axial direction.

The carriage may be further provided with at least one other rollermember arranged to contact the rod at a second angle to the axis ofrotation of the rod. In this case, the other roller member is providedwith its own actuator means arranged to press the other roller memberagainst the rod. The second angle at which the other roller member isdisposed with respect to the axis of rotation of the rod is such so asto generate a second vector component in a second axial directionopposite to the first axial direction, thus moving the carriage in theopposite direction along the rod.

The second angle at which the other roller member is disposed at withrespect to the angle of rotation of the rod may be identical inmagnitude but opposite in direction to the first angle, in which casethe speed of movement in each direction along the rod when therespective first or other roller is engaged with the rod will beidentical. Alternatively, the second angle may be different in magnitudeto the first angle, in which case the carriage will move at a differentspeed in the second axial direction when the other roller is engagedwith the rod to the speed of movement in the first axial direction whenthe first roller is engaged with the rod.

Preferably, the operations of the first and the other actuation meansare mutually exclusive, whereby only one or other of the roller membersmay be in contact with the rod at any one time.

Furthermore, the roller members need not each contact the same side ofthe rod, but may instead be disposed at any convenient location aroundthe rod. In the case where the first roller is disposed on the oppositeside of the rod to the other roller, then when the apparatus is vieweddirectly from above the first roller and the other roller may appear tobe arranged at substantially the same angle to the axis of rotation ofthe rod. This is due to the actual contact surface of the rodeffectively moving in opposite directions on each opposite side, thusgenerating axial vectors along the rod in opposite directions for thesame roller angle.

It is advantageous if the means for pressing the rotatable membersagainst the rod is in the form of a piezo electric device so that thelinear motion can be electrically controlled.

In addition, more than one roller member may be provided arranged togenerate movement in each direction. In this case, each roller memberarranged to generate movement in the same direction may be disposed atdifferent angles to each other, so that the speed of linear movement ofthe carriage in the direction may be varied by selection of theappropriate roller. Furthermore, where this is the case, the actuatormeans for each roller can be controlled independently from each other.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In order that the present invention be more readily understood, anembodiment thereof will now be described by way of example withreference to the accompanying drawings, in which:

FIG. 1 shows an exploded perspective view of a apparatus according tothe present invention;

FIG. 2 shows a diagrammatic side view of the apparatus shown in FIG. 1;

FIG. 3 shows a perspective view of a piezo electric actuator suitablefor use with the apparatus shown in FIG. 1;

FIG. 4 shows a perspective view of an alternative arrangement of theapparatus of FIG. 1, wherein the rotatable members are disposed onopposite sides of the shaft; and

FIG. 5 shows a plan view of the arrangement of FIG. 4 looking in thedirection of the arrow A.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention is arranged to producelinear motion in a controllable fashion from a shaft which is arrangedto rotate continuously in one direction.

Referring firstly to FIG. 1, this shows a rotatable shaft (10) which isarranged to rotate continuously in one direction as indicated by thearrow A. Mounted on the shaft (10) is a carriage (11) which in thisembodiment is shown as being elongate in the direction of the shaft (10)and is provided with rotatable members (12 a, 12 b) at either end of thecarriage. The rotatable members (12 a, 12 b) are coupled to the carriage(11) by means of actuators (14 a, 14 b) which, when operated, arearranged to press one or other of the rotatable members against theshaft (10).

Each rotatable member is set at an angle to the perpendicular of theshaft (10) so that an axial vector is created when a rotatable member(12) engages the shaft as a result of the operation of the respectiveactuator means for that rotatable member. The angle of the or eachrotatable member with respect to the perpendicular of the shaft ischosen having regard to the desired direction of movement of thecarriage (11) and the relative speed of linear motion as compared withthe rotational speed of the shaft. It will be appreciated that thislatter factor is affected by the magnitude of the vector created due tothe angle of the rotatable member. It will be further appreciated thateach rotatable member rotates in the same direction with respect to itsown axis of rotation as every other rotatable member, regardless of theangle at which each rotatable member is disposed with respect to theshaft. Thus, for example, if the shaft is arranged to rotateanticlockwise, then all the rotatable members will rotate clockwiseabout their own respective axes, when viewed from the same respectiveend. It is the axial component vector generated as a result of the anglewhich causes the movement of the carriage in one direction or the other,and not the direction of rotation of the particular rotatable member.

As shown in FIGS. 1 and 2, in a first arrangement the rotatable members(12 a and 12 b) are set at inverse angles to each other so that onemember generates an axial vector along the shaft in one direction whenpressed against the shaft, and the other member generates a second axialvector along the shaft in an opposite direction. The mechanism couplingthem to the carriage (11) is in the form of a piezo electric devicewhich will be described in more detail later with reference to FIG. 3.When one or other of the piezo electric devices (14 a or 14 b) isenergised, its associated rotatable member (12 a or 12 b) is pressedagainst the rotating shaft (10) to drive the carriage (11) in one orother axial direction along the shaft (10) without stopping the shaft.

It will be appreciated that various modifications can be made to theabove described arrangement. For example, although the rotatable members(12 a and 12 b) are shown in FIGS. 1 and 2 as being disposed at oppositeends of the carriage (11) and in line with each other, it would bepossible to shorten the length of carriage (11) by disposing therotatable member (12 b) at the same end as the rotatable member (12 a)but on the opposite side of the shaft to the rotatable member (12 b) sothat in effect the carriage (11) surrounds the shaft (10) which rotateswithin its confines. Such an arrangement as this is shown in FIGS. 4 and5. In this case, as the surface of the shaft (10) is effectively movingin opposite directions at each opposite side of the shaft where therotatable members respectively engage, the rotatable members (12 a) and(12 b) may each be disposed at the same angle 74 to the axis of rotationof the shaft, when viewed from either directly above or below at aperpendicular to the contact surface of either of the rollers, as shownin FIG. 5. As before, each of the rotatable members will rotate in thesame direction with respect to their own axes, but as they are onopposite sides of the shaft (10) axial component vectors in oppositedirections will be produced for each rotatable member, thus allowing thecarriage to be moved in either direction along the shaft.

It is also possible to increase the number of rotatable members forproducing motion in any one direction. In this case it is most easy toconsider a number of rotatable members (12 a) disposed around thecircumference at, for example, 120° intervals. This use of multiplerotatable members could equally be used with the short drive systemdescribed above by alternating rotatable members (12 a and 12 b) aroundthe circumference of the rod.

Where multiple rotatable members are used for producing linear motion inone direction, each of the members can be disposed at a different angleto the axis of rotation of the shaft. This has the advantage that byselecting individual rotatable members of the group to press against theshaft, the carriage may be moved along the shaft in the same directionbut at different linear speeds for the same rotational speed of theshaft. The respective actuator means for each rotatable member must inthis case be independently controllable from each other to allowdifferent rotatable members to be selected to press against the shaft.

In addition to the above, where a plurality of rotatable members areemployed, it is of course possible to have each of the members set atthe same angle, and to engage all of the members with the shaft at thesame time. This has the advantage that a greater linear driving force inthe axial direction will be generated, resulting in a more positivelinear drive.

The above description has concentrated so far on the arrangement of therotatable members with respect to the shaft. The following descriptionwill now describe in more detail the actuator means used to engage eachroller with the shaft.

FIG. 3 shows one form of a piezo electric actuator which could be usedfor pressing a rotatable member against the rotatable shaft (10). Theactuator comprises a generally flat hairpin-like resilient deviceusually formed of a spring steel or the like. The legs (31 and 32) arearranged to lie substantially parallel with each other in an engagementalong a substantial length of the legs and this in turn means that thereis a rigid connecting portion (33) joining the two legs together. Thenon-engaging surfaces of the legs (31 and 32) are each provided withpiezo electric layers (35 and 36) respectively. The piezo electriclayers are poled the same way and are electrically linked by a conductor(38). The free end of one of the legs (31,32) is fixed and when thepiezo electric layers (35 and 36) are energised the free end of theother leg is deflected away from the fixed leg. Removal of theenergisation from the device results in the legs resuming their paralleland touching relationship.

As an alternative to the above arrangement, the two legs need notnecessarily be fixed to the rigid connecting portion so that they lie inmutual engagement, nor need they be parallel to each other. Instead, thelegs may be fixed so that opposite surfaces of each leg are merelyfacing each other, and may be angled away from at each other at anyconvenient angle. Such an arrangement has a disadvantage in that it isstructurally weaker when the piezo-ceramic layers are not energised, butmay provide greater flexibility in incorporating the actuator intomechanisms as required.

Whichever of the above arrangements is chosen, it will thus be apparentthat by using a piezo electric actuator as shown in FIG. 3 for theactuators (14 a and 14 b) shown in FIGS. 1 and 2, a very simpleelectrically controlled drive mechanism can be produced which allows forclose control of which, if any, rotatable member is to be engaged withthe shaft at any one time.

Other forms of piezo electric actuator can be utilized depending on theexact application which is contemplated. For example, an actuator suchas disclosed in our International Application PCT/GB98/0670 could alsobe utilized. Moreover, other forms of actuation means may also besuitable for use with the present invention, such as, for example,electric solenoids, or pnewnatic or hydraulic actuators, again dependingupon the application to which the present invention is to be put. Theappropriate choice of actuator will be apparent to those skilled in theart with due regard to the surrounding circumstances in which thepresent invention is to be employed.

Furthermore, any of the dimensions, materials and/or scale of themechanism of the present invention may be varied at will withoutdeparting from the scope thereof as defined by the accompanying claims.

What is claimed is:
 1. An apparatus for producing linear motioncomprising: an elongate rod of circular cross-section arranged to becontinuously rotated in a first direction about an elongate axis; and acarriage arranged to mounted on the rod so as to permit axial movementof the carriage along the length of the rod; wherein the carriagecomprises: at least one first roller member arranged to contact the rodsuch that an axis of rotation of said roller member is at a first angleto the axis of rotation of the rod; said apparatus being characterizedby further comprising: at least one first piezo-electric actuator meansarranged to carry the first roller member for pressing the first rollermember against the rod to cause rotation of the roller member, saidpiezo-electric actuator means comprising a first substantially flatresilient leg member and a second substantially flat resilient legmember, said first and said second leg members being connected by asubstantially stiff bight portion, said leg members being arranged tolie substantially parallel with opposite surfaces of each leg member inmutual engagement along a substantial length of each leg member, othersurfaces of each leg member being provided with piezo-electric layersarranged to deflect each leg member away from the other respective legmember; wherein the rotation of the roller member generates at least oneaxial vector in a first axial direction along said rod whereby to causemovement of the carriage along the rod in said first axial direction. 2.An apparatus according to claim 1, wherein the carriage furthercomprises: at least one other roller member arranged to contact the rodsuch that an axis of rotation of said other roller member is at a secondangle to the axis of rotation of the rod; and at least one otherpiezo-electric actuator means arranged to carry the other roller memberfor pressing the other roller member against the rod to cause rotationof the other roller member; wherein the second angle is such that therotation of the other roller member when pressed against the rodgenerates a second axial vector in a second axial direction.
 3. Anapparatus according to claim 2, wherein the carriage further comprises aplurality of said other roller members and a corresponding plurality ofsaid other piezo-electric actuator means.
 4. An apparatus according toclaim 3, wherein each of said plurality of other roller members isarranged to rotate about an axis disposed at a different second angle tothe axis of rotation of the rod than every other roller member.
 5. Anapparatus according to claim 3, wherein two or more of said plurality ofother roller members are arranged to rotate about an axis disposed atthe same second angle to the axis or rotation of the rod.
 6. Anapparatus according to claim 3, wherein each of said plurality of otherpiezo-electric actuator means are independently controllable to allowone or more of said other roller members to be pressed against said rodat any one time.
 7. An apparatus according to claim 2, wherein saidfirst roller member is arranged to contact the opposite side of said rodthan said other roller member.
 8. An apparatus according to claim 2,wherein the second angle of said other roller member and the first angleof said first roller member are identical whereby said second axialvector is identical in magnitude to said first axial vector.
 9. Anapparatus according to claim 2, wherein the second angle of said otherroller member and the first angle of said first roller member are notidentical, whereby said second axial vector is not identical inmagnitude to said first axial vector.
 10. An apparatus according toclaim 2, wherein the carriage further comprises a plurality of saidfirst roller members and a corresponding plurality of said firstpiezo-electric actuator means.
 11. An apparatus according to claim 1,wherein the second angle of said other roller member and the first angleof said first roller member are identical whereby said second axialvector is identical in magnitude to said first axial vector.
 12. Anapparatus according to claim 1, wherein the second angle of said otherroller member and the first angle of said first roller member are notidentical, whereby said second axial vector is not identical inmagnitude to said first axial vector.
 13. An apparatus according toclaim 1, wherein the operations of said first piezo-electric actuatormeans and said other piezo-electric actuator means are mutuallyexclusive whereby only one of said first roller member or said otherroller member may be pressed against said rod at any one time.
 14. Anapparatus according to claim 1, wherein the carriage further comprises aplurality of said first roller members and a corresponding plurality ofsaid first piezo-electric actuator means.
 15. An apparatus according toclaim 14, wherein each of said plurality of first roller members isarranged to rotate about an axis disposed at a different first angle tothe axis of rotation of the rod than every other first roller member.16. An apparatus according to claim 14 wherein two or more of saidplurality of first roller members are arranged to rotate about an axisdisposed at the same first angle to the axis of rotation of the rod. 17.An apparatus according to claim 14, wherein each of said plurality offirst piezo-electric actuator means are independently controllable toallow one or more of said first roller members to be pressed againstsaid rod at any one time.
 18. An apparatus according to claim 17,wherein the carriage further comprises a plurality of said other rollermembers and a corresponding plurality of said other piezo-electricactuator means.
 19. An apparatus according to claim 17, wherein thecarriage further comprises a plurality of said other roller members anda corresponding plurality of said other piezo-electric actuator means.20. An apparatus according to claim 1, wherein a free end of said firstleg member is fixed to said carriage and a free end of said second legmember is arranged to carry at least one of said roller members.